July, 1927
INDUSTRIAL A N D ENGINEERING CHEMISTRY
777
Treatment of Water to Prevent Corrosion’ By John R. Baylis 6938 CRANDON A v E . , CIlICAGO, ILL.
No treatment of water will prevent corrosion of iron HE chemical treatment At that date the electrowhere a fresh metal is exposed. Water a t the solubility of public water supchemical theorg of corrosion equilibrium of calcium carbonate and containing over plies ten years ago was had not gained wide accept25 p. p. m. of CaC03 will precipitate calcite where primarily for the removal of ance, and many were still of corrosion takes place and aid in forming an impervious turbidity and bacteria. Here the opinion that a free acid protective coating. and there a few hard waters sufficient to produce an acid The most durable practical coating, with the possible were being softened, but even reaction with methyl orange exception of cement lining, does not last many years in for most of these softened supor erythrosin indicators was corrosive water, but any coating that lasts till a proplies the major problem was a n e s s e n t i a l f o r iron to tective film is built up from the constituents of the to make the water clear and corrode. The excellent artiwater will give good protection when the water is more pure. Until recently, little cles by Evans,4 M c K a y , alkaline than the saturation equilibrium of calcium thought has been given to A s t o n , 6 W i l s o n , ’ Speller,* carbonate. To waters with less than 25 p. p. m. of p W h i t m a n , R u s s e l l , and the effect of the water on CaC03 lime should be added to produce the desired pipes and other conduits. i i l t i e ~ i and , ~ others now give alkalinity. To others either lime or soda ash may be Deterioration was thought to us a fair conception of the L added. be something that could not corrosion problem. Iron and For corrosive water such as is found in New York, be avoided with the matezinc tend to dissolve or comAtlanta, and many other cities it is believed that a fair rials used, and very little bine with water and liberate estimate of the loss due to the corrosive property of effort was made to treat the hydrogen gas. The life of the water is at least $1.50 per capita annually. water to lessen it. There has these metals exposed to water All evidence indicates that iron pipe, whether galbeen a feeling that some one depends almost entirely on vanized, painted with coal-tar pitch, or cement-lined, would eventually develop a protective coatings, for if a is durable only when the water is saturated with calm a t e r i a l which would not fresh surface of either was cium carbonate or is more alkaline. deteriorate appreciably when kept exposed to the water of e x p o s e d to water. So far any of our public supplies, this dream of the ideal metal a t a price within reasonable the destruction of the metal would be entirely too rapid for bounds has not been realized; neither does the possibility practical uses. The stirring up of the sleeping ingredients of findjng a durable coating for iron pipe offer very much of the water by filtration as stated by Haaen is really the encouragement, product’ion of conditions less favorable for the formation More and more it becomes evident that the problem is of a protective coating. The problem of pipe protection one for the water chemist to solve by treating the water is largely the establishment of conditions that will produce to prevent deterioration of the pipes rather than to continue a well-adhering surface coating over the metal. searching for non-corrosive materials. pH and Solubility of Zinc Hydroxide Probably the first attempt to reduce corrosion on a large The mriter’o has shown that p H of about 6.5 is the critscale by chemical treatment of the water was at Baltimore2 in 1920. It is true that alkalies had been used in a number ical point for zinc. When it is below this figure, a large of supplies prior to this, but in practically all such instances amount of zinc will be found in solution when equilibrium the purpose was to aid coagulation and not primarily t o is established. The soluble zinc is due, not to the oxide, prevent corrosion. This is true especially when lime is but largely to salts of zinc. The writer does not have exact used with sulfate of iron for clarifying turbid waters. The figures as to the amount of zinc that will exist in solution water is usually left fairly non-corrosive by such treatment, as the hydrous oxide when the pH is above 7.5, but it apbut the lime is applied mainly to aid in the production of a pears to be considerably less than 1 p. p. m., perhaps as low as 0.1 p. p. m. The saturation equilibrium of zinc satisfactory hydrous ferric oxide precipitate. hydroxide is usually given as higher than this figure; however, Non-Corrosive Water experiments do not seem to confirm such high results when It is well known both to engineers and chemists that the p H is 7.5 or over. Regardless of what the solubility some natural waters are not very corrosive to iron pipe, equilibrium may be, it is evident that zinc does not corrode but the reason is not so well known. The wide variation very rapidly when exposed t o water which is above this in the concentration of soluble salts in these non-corrosive figure. There are a number of water supplies in which the pH waters has led many to believe that there is some unknown factor controlling the corrosion. Hazen,3 in 1921, stated is below 7.0, and in these supplies part of the zinc in solution that the soft and corrosive waters are generally near the probably exists as some compound such as the sulfate, coast, and that the Great Lakes water is always non- chloride, or carbonate. If an alkali is added to a solution corrosive. He could offer no explanation but said that of zinc salt, such as the sulfate, a precipitate of hydrous + J . SOC.Chem. I n d . , 43, 320T (1924); THISJOURNAL, 17, 363 (1925). in some way the chemical treatment of many of the public 5 Trans. A m . Elecfrochem. Soc., 41, 201 (1922); Thompson and *McKay, water supplies stirs up the sleeping ingredients of the water THISJOURNAL,16, 1114 (1923). and makes them aggressive. 6 Trans. A m . Elecfrochem. SOL.,41, 201 (1922).
T
Received February 9, 1927. Presented before the Division of Water, Sewage, and Sanitation a t the 73rd Meeting of the American Chemical Society, Richmond, Va., April 11 t o 16, 1927. Baylis, J . A m . Water Works Assoc.. 9, 408 (1922). * Trons. A m . SOL.Cinil Eng., 85, 482 (1922).
7 THIS JOURNAL,15, 127 (1923). 8 “Corrosion-Causes and Prevention,” McGraw-Hill Book Co., Inc., liew York, 1926. Q THIS JOURNAL,16, 665 (1924). 10 J . A m . W a f e r Works Assoc., 16, 598 (1926).
778
I-VDUSTRIAL AND ENGINEERING CHEMISTRY
oxide of zinc is produced and the solution will reach an equilibrium in which the p H is belo? 7.5, or even 7.0, if much of the salt still remains in solution. I n other words, it is not possible to have a solution above about 7.5 in which zinc sulfate exists to any great extent, though the amount of soluble zinc may be over several parts per million in such an experiment. Any zinc going into such a solution from the metal apparently does not form some soluble salt but the insoluble hydrous oxide, whereas if the pH is below about 6.5 it will not form the oxide but some fairly soluble salt. This applies to pH values within the ranges found in public water supplies and may not hold for very alkaline solutions. There is a fairly wide space between p H of 6.5 and 7.5, and more exact figures may narrow it somewhat. One thing of importance is known-with most maters where the pH is 6.5 and below, the zinc galvanizing on iron pipes corrodes fairly rapidly, and where it is 7 . 5 and above, the galvanizing has a long life. This applies to cold water lines or where the temperature is below about 60" C. It has been shownll that for higher temperatures the tendency for zinc to corrode is very much greater than for low temperatures. This, however, may not affect the solubility of the oxide of zinc very much, for the difference in the rate of corrosion may be due more to the failure of the oxide to form an impervious coating than to a great change in the solubility Concentration. Corrosion of Fresh Iron Surface Not Prevented by Water Treatment
There is no treatment which may be applied to water for domestic use that will prevent corrosion where a fresh iron surface is exposed. Protective coatings are built up very slowly, and if iron pipes which have no coating are used they will usually form tubercles before a protective coating can be formed from the constituents of the water. Protective coatings applied by the manufacturer, such as galvanizing, cement, or paint, are essential, but with the exception of cement these coatings merely delay corrosion until a protective coating of a more durable nature is formed. It is true that under the durable coating we may find the galvanizing, paint, or other coating still there after many years of service, but this is because the built-up coating has protected it and not because it is so durable. The purpose of water treatment is to protect the protective coatings and avoid any tendency to form tubercles. Once a tubercle has formed it is hard to stop corrosion underneath it, for conditions are produced within the area covered by the tubercle which are favorable for corrosion to continue, even though the water is alkaline. Relation of CaC08 Solubility Equilibrium to Solubility of Fe(OH)2
It is known that the saturation equilibrium of ferric hydroxide in water which is within the ranges of our domestic supplies is very low. Ferrous hydroxide is more soluble; however, its saturation point appears also to be low when the p H is above 8.0. It has been shown1* that not over about 0.1 p. p. m. of soluble iron (Fe) will exist in solution in the absence of oxygen when the p H is above the solubility equilibrium curve of calcium carbonate, as shown in Figure 1, but below this point increased amounts of soluble iron will be found as the distance from the curve increases. Whatever the tendency to force iron into solution, nearly all of it will be precipitated as a hydrous ferrous oxide when the p H is above the curve. 11 12
Baylis, Mech. Enn., 48, 1133 (19261. Baylis. THISJ O U R N A L , 18, 370 (1926)
Vol. 19, No. 7
The solubility concentration of ferrous hydroxide or the hydrous oxide is of great importance in the corrosion of iron, for as a rule no oxygen is present a t the metal surfaces where corrosion is taking place. Dissolved oxygen may have considerable influence in throwing the soluble ferrous hydroxide out of solution as the hydrous ferric oxide, in combining with nascent hydrogen, and in the production of cathodic materials or areas; but where the iron is actually going into solution no oxygen is present at the metal surface and the solubility of ferrous hydroxide plays an important part. I n stating the soluble compound to be ferrous hydroxide, the writer is using the customary expression. He has no information as to whether it is ferrous hydroxide or a hydrous ferrous oxide. The concentration of negative ions such as the sulfate and chloride in the solution adjacent to the metal surface frequently reduces the pH to the point where considerable ferrous iron will exist in solution, even though the solution outside of the iron rust is at a much higher pH-that is, more alkaline. The soluble iron in this case is present largely as some compound other than ferrous hydroxide. If it were not for the concentration of sulfates and chlorides near the metal surface the tendency would be for the solution to establish itself at an equilibrium where very little iron will remain in solution. This may not be the case for distilled water, but it holds for all domestic supplies. If salts that are not frequently found in potable water are excluded, it'might be said that if the water is free from sulfates and chlorides very little corrosion and practically no pitting will take place. This probably will not hold if a large amount of free carbon dioxide is present. Frequently a large part of the surface of iron exposed to water becomes passive-that is, corrosion nearly ceases. This is usually explained as being due to the production of cathodic areas, but it is more likely to be due to the formation of an impervious coating. IO
9
8
I a 7
6
0
50
100
150
200
250
300
350
ALKALINITY, P P M
F i g u r e 1-Approximate
S o l u b i l i t y E q u i l i b r i u m of C a l c i u m Carbonate
After pitting and tuberculating have started-that is, after sulfates or chlorides have concentrated in the solution against the metal surface-the only hope of stopping corrosion is by producing an impervious membrane a t the outer surface of the precipitated iron rust. Regardless of the p H and alkali concentration of the solution outside of the pit and tubercle, the pH on the inside is usually less than 7.0, and is believed to be near 6.0 for active pits. In the production of an impervious membrane a t the outer surface of tubercles the solubility equilibrium of ferrous hydroxide plays an important part, for when the ferrous iron diffuses to where the outside solution has an influence, it is desirable that this solution be such that, in the absence of oxygen, very little soluble iron will exist. Then the tendency will be to precipitate the iron as soon as it reaches the outer surface of the tubercle.
INDUSTRlAL A N D ENGINEERILYGCHEMISTRY
July, 1927
Tendency of-Corroding Iron to Precipitate CaCO8 The majority of waters suitable for domestic use are below the saturation point of calcium carbonate-that is, they are more acid and would dissolve calcium carbonate if it were present in the solid form. Waters that are on the curve shown in Figure 1, or above, are usually not corrosive to iron water pipes which have some kind of a protective coating. The Great Lakes water, being non-corrosive, is slightly above the curve most of the time, and should it go below it is so near the curve that there is very little tendency to corrode. The following analysis of sediment from pipes in Chicago shows that the water is gradually precipitating calcium carbonate: Per cenl 52 2 3.7
J n w.~ l u~~. h l~. e -~~
Iron and a!uminum oxides
30.3 13.8
Calcium carbonate Magnesium carbonate
Corroding iron has the power of removing all the free and most of the half-bound carbon dioxide in the water, and when there is considerable calcium bicarbonate present a supersaturation of calcium carbonate is produced, part of which will be precipitated. If over about 25 p: p. m. of calcium carbonate are present, part will be precipitated fairly rapidly, but after this concentration is reached the rate slows up materially and may require some time for the concentration to be reduced to 15 p. p. m. The rapid reduction for water high in alkalinity is shown by the following figures: TIMEIS CONTACT WITH I R O N
ALKALINITY
PH
P. P . m. 0 45 1 11/2
2 3
minutes minutes hour hours hours hours
128
7.5
22
8.7 8.8 8.8
8.3
65 50 40 25
...
The water in this case was in contact with a large amount of iron lathe turnings freshly cut from a wrought-iron pipe. This gave a I-ery large surface area in proportion to the volume of water. The flask was agitated frequently and the water poured out a few times for about a minute each time to hasten corrosion by oxidation of the nascent hydrogen. Such a rapid reduction in alkalinity is not duplicated in a pipe, except possibly in the film of water adjacent to the iron surface. The following figures show that the alkalinity of the water in a l/r-inch iron pipe is reduced and, if' time is allowed, it will be reduced quite low: TIMESTANDING 0 minutes 7 days
ALKALINITY 4 i p. p. m. 13 p. p. m.
PH 8.3
8.6
TOTAL, HARDNESS 53
18
Water that is a t the solubility equilibrium of calcium carbonate and contains over about 25 p. p. m. of calcium carbonate will precipitate calcite crystals where corrosion is taking place and the calcium precipitate will aid materially in the formation of an impervious coating. The corroding iron combines with the half-bound carbon dioxide and thereby produces a supersaturation of calcium carbonate. When the calcium carbonate alkalinity is below about 25 p. p. m. there is not enough present for i t to aid very much in the formation of a n impervious film, and such films as are produced are composed almost entirely of iron rust. For some fairly hard waters calcium carbonate will be precipitated in the iron rust when the water is slightly corrosive to calcium carbonate, but this precipitate will exist only where it is protected by the precipitated iron oxide.
77F
For the vast majority of wateEs, especidly those containing less than 50 p. p. m. of calcium carbonate, very little aid to the prevention of corrosion can be expected from this source. The safest assurance that calcium carbonate will aid in the production of an impervious film is to have the water at least saturated with this compound, and it is better for it to be slightly supersaturated part of the time. The most durable coating which is practicable to apply to pipe, with the exception of cement linings, does not last many years in corrosive water, whereas most any kind of a coating having a life sufficient to allow a protective film to be built up from the constituents of the water will give good protection to cold-water pipes when the water is more alkaline than the saturation equilibrium of calcium carbonate. Zinc coatings appear to be reasonably well protected when the water is just a little below the curve shown in Figure 1, or more alkaline, but the safest plan, even for galvanized pipe, is to have the water a t the saturation equilibrium of calcium carbonate. Coal-Tar Coatings
Not much is known about the life of coal-tar coatings which are applied on cast-iron pipe, except that they are not durable in moderately corrosive water. Old cast-iron pipes which have been removed from the distribution systems in many cities reveal the fact that little or none of the original coating remains. There is Borne evidence that a coating of the thickness ordinarily applied is not entirely watertight but is slightly porous, Whether this is true or whether holes soon form in it, it is evident that such coatings are not durable in corrosive water, and they may be expected to break down within five to ten years. The coating is not all removed in this time but tubercles are formed in the pipe. It may be possible to find means of applying thicker and more durable coal-tar or asphalt coatings, but those now being applied are not meeting the service desired of them in corrosive water. Where the water is non-corrosive, coal-tar coatings appear to be in good condition after twenty-five years or more of. service. I n fact, coatings have been found to be in good condition after fifty years where they are well protected. There may be holes through the old coating, but they are sealed shortly after being formed and practically no corrosion of the pipe occurs. Cement-Lined Pipe Portland cement mortar for lining iron pipes gives promise of being one of the best coatings for the inside of pipes carrying water at ordinary temperature, or perhaps as high as 60" to 70' C. Cement-lined pipes have been in use in some cities for more than fifty years, but owing to the difficulty in applying the lining they have not been extensively used until recently. The research department of the American Cast Iron Pipe Company developed the centrifugal method of applying cement linings a few years ago and since then the use of such pipe has increased rapidly. It is now the hope of many waterworks officials that this will solve the corrosion problem. Without doubt it is an improvement over the other coatings ordinarily used in that i t has a very much longer life, but it is not permanent in corrosive water unless fairly thick. There is also the problem of protecting the ends of pipes where they have been cut after the lining has been applied, as well as the couplings and small specials in threaded pipe which may be quite numerous even in the plumbing of an ordinary residence. Hydrated Portland cement gives up calcium hydroxide very rapidly when exposed to water and produces a solution against the iron surface of the cement-lined pipe that is approx-
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
itnately saturat.ed witli limewater when the coating is first applied. 'This alkalinit,y is high enough to stop rorrosion in a very short time. The surface of concrete exposed to the air or water docs not long remain at it,s high alkali concentration. If it isexpos& to the air, which is the case for all cement linings hcfore tlie pipes are placed into service, some of tlie Iiigli-oaloium coini)ounrls will be carbonated. In stating that a calcium ompo pound in cemeut is carbonated, it is meant, that, tlie calcium lias becn released from its harid with the silks or aluinina and has united with carbon dioxide. The final pruilurt of nearly all tlie calcium in cemerit exposed to tlio air is calcium carbonate with possibly some low-cnloiuni coinpoutid of silica and alumina, though the eriileiice indicates that, e\-en all the monocalcium silir:at.e and aluminate are bruiien down. The depth to \d,icli carbon dioxide will penet,rate int,o concrete dcpeiids on its porosity. I n concrete, as it is usually mnniifnoturcd. tiic mrbori dioxide will penetrate froin one-half to one inch within two or three years, and in conc r e t e mixed fairly wetitmaypenetrate mucli further. The c o n c r e t e biock on tlie right in Figure 2, which is about 6 inches square, wzs cut from an important structure about one year after the concrete had been poured. It mas then stored in a room in the i;tboratory for I'iwre >-Penetration of Carbon Dioxide another year. T h e into ConcrDte 'lock O n the left was prepared especially for test purposes and was approxirnately one year old. It was made as dense as would be practicable to mariufacture concrete. The Mocks were broken in two and a solution of phenolphthalein was added to the surface. The area near tlie outer surfaces which did trot stain pink with the solution indicates the penotrktioii of the carbon dioxide into the concrete. In this area d l the high-calcium compounds have been carbonated. The carbon dioxide has penetrated nearly one inch into t,lie block on the right and over l/< inch into tlie one on tlie lelt. Tlie centrifugal method of applying cement linings may make the mortar very derise aud the penetration may be slower than ior concrete as usually mauuiactured. A thin cement lining Ervin to inch in thickness m:w be conipletely carbonated before the pipe is put into service. This reduces its power to inhibit the corrosion of the iron, but because the solution wit.hin the pores of t.lie cement is at least as alkaliiie as the calcium carbonate at its saturation point. and usually higher, any iron going into solution will probably be precipit.atcd within the pores of the lining. If the high-calcium compounds have not been carhooated before the pipe is put into service tliere is a tendency to form arj impemions coat,ing of calcium carbonate near tlic water surface, which keeps the solution very alkaline on the inside. Then, if the water is riot corrosive to caicium carbonate, the lining will remain in this condition indefinitely and will offer permancnt protection to the iron. When the water is corrosive to calcium carbonate there will be a gradual solution of the lime in the cement. Fortunately, the compounds remaining after the calcium and other alkalies have been leached out usiiaily adhere with sufficient strength
T'ol. 19, No. 7
to remain in place if there is no abrasion or other force tending to remove the coating, and thus greatly retard the rate a t which the water can attack the cement. The examination of ccment-lined pipe irom Danvers, Mas., kindly furnished the writer by Mr. Carson, showed that for pipes which have been in service ior fifty years the iron was well protected where t,he lining was '/a inch or more in thickness. One of the most interesting things revealed by the examination was a hard and impervious membrane of iron rust within, but usually near tho outer surface of, the liiiing, somewhat like that found over dormant tubercles. This did not occur where the solution in tlie cement was still alkaline to phenolphthalein hut where the calcium had nearly all carbonated or leached out. This mcmbrane is usually formed vithin the interior of the cement lining and it does not materially rou&en the inside surface of the pipe so as to cause increased friction as is the case with tubcrciilated pipe. Cement linings can be made tliiok enough to offer protection to iron pipe for a great many years, but there is some poitit in the corrosiveness of water at which it is more ecnomical to t,reat the water than t.o keep increasing tlie t,hickness of the lining. A l'/,inch iron pipe is required for a 1-inch opening if the lining is only I/& inch thick. Colisidering the distribution system as a whole and the number of unprotected joints that are necessary within most buildings, it is believed that i t is more economical to treat the water to the saturation equilibrium of calcium carbonate than to leave i t more corrosive. Under such conditions cement linings probably would last severa1 hundred years; however, tliere is no objection to such a long liie. This, of course, does not take into consideration corrosion from the outside. Ideal Chemical Balance in Water Sstucilted with CaCO,
Tlie saturation point of calcium carbonate depcnds on the pH, alkalinity, and to a certain extent on tile other salts in solution. The curve in Figure 1 is the approximate equilibriutn when distilled water is used and most natural waters suitable for public supplies have an equilibrium not far from t,he curve. Taking everything int.0 consideration, evidence indicates tilat ,"ator saturated ,,.it,h calcium carbooate iairly good resistance to the eorrosion oi iron aud it does not fill the pipes with a lime incrustation &s is the case wlien it is more alkaline. It is true that better protect,ion to the iron is obtained ii the mater is slightly supersaturated with calcium carbonate, but the limestone incrustation should not he pormitt,ed to build up too thick. It might be advantageous to treat the water until a calcium carbonate coating oovers entire surface, then adjust the equilibriulu of t,lle ,vat,er to where it neither precipitates calciuln nor dissolves t ~ l ecoating alreariy I'or naters below the saturation equilibrium calcium carbonate the clleapest means of making it more akaline is to add but may not be most desirable treatment, Increasing the calcium increases t,lle hardness, and costs for soap, for boiler etc, tjqien calcillm carbonate concentration is less than about 25 p, p, m,, it is believed that lime shouid he in tile proper adjustment. \+,hen higher than this it be cheapest, if a large amomit of the is used ior boilers, to treat with sodiuln carbonate or sodium hydroxide. I n this case the water should be brought to the saturation equilibrium oi the calcium carbonate present. The curve of ideal balance will then vary somewhat from the one shown in Figure 1, depettdiiig on the amount of sodium present.
J d y , 1927
IiYDCSTRIdL A S D EK’GISEE’RIXG CHEMISTRY Economic Considerations
Corrosion of iron is costing a sum far greater than is generally believed. Taking all factors into consideration, such as pipe repairs, loss of water through leaks, damage to property, the necessity for larger pipes when it is known that the carrying capacity will be greatly reduced by the formation of iron rust, fire losses due to inadequate water pressure caused from a partial stoppage of the mains, staining of bathroom fixtures and clothes being laundered, and other losses, the total economic loss due to corrosion is quite large. For corrosive water such as is found in a number of cities, it is beliered that a fair estimate of the loss is a t least $1.50 per capita annually. This figure is merely a guess, but those who have had to pay a plumber for repairing leaks or removing corroded pipes will realize that i t takes only a few leaks in a lifetime to make the repair cost as much as is figured. At Baltimore the cost of lime to make the water fairly non-corrosive has averaged about two cents per capita annually for the past three years. To this should be added a cost estimated to be less than ten cents per capita for the increased hardness. If a non-corrosive water will reduce the total losses due to corrosion one-half, which the writer feels confident it will where the water is originally very corrosive, the saving will be from 50 to 75 cents per capita annually. Corrosive water is not satisfactory to the users. and while it is difficult to estimate the value
781
of satisfaction, it may be a sum even more than the total losses due to corrosion. Iron will probably continue to be the most extensively used material for n-ater pipes. Whether it is galvanized, painted with coal-tar pitch, or cement-lined, evidence indicates that it is durable only when the water is saturated with calcium carbonate or more alkaline. Then i t seems that the economical limit of treatment should be somewhere near the saturation point of this compound, or perhaps just slightly more alkaline. Regardless of the source of supply, i t is believed that water which is corrosive to calcium carbonate should be treated, unless i t is a small supply where the cost of treatment would be excessive. TT’aterworks officials are beginning to recognize the value of chemical control for the prevention of corrosion and tuberculation of water mains. I n the few cities where it has been tried, the treatment suggested in this paper has been found of decided economic value. Not only this, but the water is more satisfactory to the users than it was before starting the treatment. Some of our most palatable spring waters are a t approximately the saturation equilibrium of calcium carbonate, and no one should hesitate to add lime or soda to drinking water. Even if the use of cement-lined pipe proves to be the solution of the corrosion problem, there are many million dollars worth of iron pipe not lined with cement now in service and in need of protection against corrosion.
Cement-Lined Water Mains’ By Harry Y. Carson AMERICAN CAST IRON P I P S CO., BIRMINGHAM, ALA,
of commercially lining castOME municipal water The purpose of this paper is to consider the factors in iron pipe with cement, it aps u p p l i e s of low alkamunicipal water supplies which contribute to so-called linity a r e n o t only pears that this development “red water” troubles and to discuss the value of a cehas yielded an a c c e p t a b l e ment lining for preventing tuberculation and internal troublesome from the standpoint of producing tubercles solution to an old waterworks corrosion of iron pipes. (Figure l), but are also corproblem, increasing the duExamples of the great durability of some early cement rosive t o the calcium comrability and service value of linings as invented and put into use a half-century ago pounds in cement. When in New England are first given, after which the mechancast-iron pipe for handling Portland cement is used as ism of the corrosion factors of water as they relate to t u b e r c u l a t i n g waters and, above all, preventing loss of an inside coating for castcement-lined iron pipe are discussed. iron pipe, a fortunate chemThe calcium hydroxide in the fresh cement lining is capacity due to tuberculation. ical reaction takes place a t capable of raising the initial water that enters the ceMethods of Manufacturing the surface of the cement ment to a high pH value. It follows that there is diffuCement-Lined Pipe which retards the action of sion of calcium to the water and this accounts for a Cement lining in iron pipe the water both on the cement constant lowering of the alkalinity of the cement until itself and on the iron. Ferrous has been used in this country, final equilibrium is established. Thereafter corrosion hydroxide, precipitated from and tuberculation take place on the iron under the ceespecially in New England, the flowing water in the main, for more than eighty years. ment in a rather unexpected manner. The cement is enters the outer pores or capnot easily flaked off by the rust. At least four general methods illaries of the cement. The of applying cement to iron ferrous hvdroxide seems to expipe have been in practice. change places with a certain amount of calcium hydroxide. The earliest, and undoubtedly the first, method was inafter which the diffusion of calcium to the water is greatly vented by Jonathan Ball as early as 1845. It consisted in slackened. I n fact, the general function of the cement lin- forming closely riveted cylinders of wrought sheet iron, 7 or ing on the inside of iron pipe seems to be one of greatly 8 feet in length and in diameter from 1 to 11/2 inches greater retarding the ordinary mechanism of corrosion in a more than the clear bore of the lining. The pipe was then set uppositive manner than is done by other forms of commercial right and a straight cylinder of diameter equal to the desired coatiiigs. bore of the pipe was lowered to the bottom of the pipe. Some From the data which have accumulated on the subject specially mixed hydraulic cement mortar was then poured into the pipe and the cylinder, which had a cone-shaped top 1 Received March 29, 1927 Prebented before the Division of Water, and guiding spurs to maintain a central position in the shell, Sewage, a n d Sanitation a t the 73rd Meeting of the American Chemical Society, Richmond, Va , April 11 to 16, 1027. was drawn up through the mortar. A rather uniform lin-
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